Stefan Dimov

Stefan Dimov
University of Birmingham · School of Mechanical Engineering

Dipl. Eng, PhD, DSc

About

279
Publications
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Publications

Publications (279)
Article
Full-text available
Super-hydrophobic textured surfaces reduce hydrodynamic drag in pressure-driven laminar flows in micro-channels. However, despite the wide usage of non-Newtonian liquids in microfluidic devices, the flow behaviour of such liquids was rarely examined so far in the context of friction reduction in textured super-hydrophobic micro-channels. Thus, we h...
Presentation
Laser Induced Periodic Surface Structures (LIPSS) and Direct Laser Writing (DLW) enable the selective fabrication of micro/nano surface structures on a broad range of materials. Such engineered surfaces can be tailored and have demonstrated various functional responses, from optical to hydrophilic/phobic and non-fouling properties. One still limiti...
Article
Surfaces covered with micro, nano and multiscale topographies are the subject of significant interest due to their ice-repellency properties in the last decade. Ultrafast laser processing is becoming a widely used clean manufacturing technique to fabricate ordered nano and multiscale topographies on metallic surfaces over relatively large areas. In...
Article
Surface patterning has been used to enhance the fracture toughness of adhesive joints. In this study, the effect of the variable bondline thickness introduced by the patterns and the effect of pattern geometry on the fracture behaviour of adhesive joints were analysed. Surface patterns including longitudinal grooves, transverse grooves, dimples and...
Article
Adhesion of viscous liquids on packaging surfaces could lead to wastage, an increase of recycling costs, and even customers' dissatisfaction in applications related to food, cosmetics and agrochemical industries. Lubricant-impregnated surfaces (LIS) gained much attention recently over other surface functionalisation technologies due to their non-st...
Article
Adhesion of viscous liquids on packaging surfaces could lead to wastage, an increase of recycling costs, and even customers' dissatisfaction in applications related to food, cosmetics and agrochemical industries. Lubricant-impregnated surfaces (LIS) gained much attention recently over other surface functionalisation technologies due to their non-st...
Article
Laser surface patterning has attracted a significant interest from industry and research due to its promising applications in surface functionalisation. However, there are specific issues and limitations associated with the beam delivery, especially when processing 3-D surfaces and/or setting up routines for executing complex multi-axis processing...
Article
Full-text available
Ice accretion on external aircraft surfaces due to the impact of supercooled water droplets can negatively affect the aerodynamic performance and reduce the operational capability and, therefore, must be prevented. Icephobic coatings capable of reducing the adhesion strength of ice to a surface represent a promising technology to support thermal or...
Article
Textured superhydrophobic surfaces (TSS) are purported to reduce flow friction in microchannels due to velocity slip at liquid-gas interface. At the same time, the liquid-gas interface inhibits heat transfer in textured microchannels due to the low thermal conductivity of entrapped gas phase. Despite significant understanding on fluid flow and ther...
Article
Full-text available
Any processing disturbances in laser surface texturing (LST) could compromise the resulting surface topography and thus their desired functional response. Disturbances such as focal plane offsets and beam incident angle variations are always present in LST processing of 3D parts and can affect the surface morphology. In this research the effects of...
Conference Paper
Inspired from the dewetting properties of Lotus leaves, the fabrication of dual micro/nano-scale topographies is of interest for many applications. In this research, superhydrophobic surfaces are fabricated by a process chain combining ultrashort pulsed laser texturing of steel inserts and injection moulding to produce polypropylene parts. This man...
Article
Full-text available
The paper reports an investigation on the mechanical durability of textured thermoplastic surfaces together with their respective wetting properties. A range of laser-induced topographies with different aspect ratios from micro to nanoscale were fabricated on tool steel inserts using an ultrashort pulsed near infrared laser. Then, through micro-inj...
Article
Research article published as part of Special Section Papers of Journal of Micro- and Nano-Manufacturing 7(1) 010901. Abstract: Functionalized metallic nano-features can be selectively fabricated via ultrashort laser processing, however the cost-effective large-area texturing, intrinsically constrained by the diffraction limit of light, remains a...
Conference Paper
Full-text available
The large area uniformity of laser-induced periodic surface structures (LIPSS) on ferritic stainless steel and titanium alloy is studied. A single-step process was designed to generate low spatial frequency LIPSS (LSFL) over relatively large areas. For the first time, a new LIPSS morphology is fabricated using near-infrared ultrashort pulsed laser....
Conference Paper
Full-text available
The direct laser submicron texturing of X6Cr17 stainless steel plates is reported. A hexagonal close-packed monolayer transparent silica microspheres deposited onto the metallic surface was irradiated with near-infrared femtosecond laser source to generate an array of Photonic Jets (PJ). The PJ intensity profiles were calculated by simulation. PJ f...
Article
Full-text available
In the present work, a study of laser-based surface structuring of aerospace-grade titanium alloy (Ti-6Al-4V) with subsequent ageing by employing two different storage methods is undertaken. The titanium alloy samples were patterned using UV-ns and IR-fs pulsed lasers in a two-step process to fabricate bio-inspired hierarchical structures. The resu...
Conference Paper
Full-text available
This paper presents an experimental study about the effects of micro-textured surfaces on wetta-bility and spreading of lubricant versus the tribological effects. Starting with the ultrashort pulsed laser texturing of martensitic steel surfaces, tribological characterization are performed on three geometrical patterns. Experiments are carried out o...
Article
Laser-induced oxidation of metallic surfaces such as titanium is used in many application areas for colour marking due to its selectivity, cleanness and processing speed. However, as the generated colours are permanent this reduces the flexibility and applicability of this laser processing technology. Therefore, a method is reported in this paper t...
Article
The paper reports a laser patterning method for producing surfaces with dual scale topographies on ferritic stainless steel plates that are hardened by low temperature plasma surface alloying. Nitrogen and carbon based gasses were used in the alloying process to obtain surface layers with an increased hardness from 172 HV to 1001 HV and 305 HV, res...
Article
Laser induced ripples (also known as Laser Induced Periodic Surface Structures, LIPSS) have gained a considerable attention by both researchers and industry due to their surface functionalization applications. These ripples act as diffraction gratings for the visible light therefore it is widely used in some optical applications and color marking....
Article
Purpose: The purpose of the present work was to achieve fast and more precise ablation in dentin and enamel by using a commercial femtosecond laser system with high repetition rate, whilst avoiding any collateral irreversible damages in the hard tissue and pulp area. Methods: We used fluence of the incident laser pulses which was marginally high...
Presentation
The aim of the research is to develop hybrid additive-subtractive manufacturing solutions for automotive, railway and space applications by combining machined ‘preforms’ or metal injection moulded (MIM) parts with more complex selective laser melted (SLM) structures on top of them. The hybrid process chain involves use of modular workpiece holding...
Article
Processing technologies that engineer surfaces with sub-micron topographies are of a growing interest to a range of optical, hydrophobic and microbiological applications. One of the promising technologies for creating such topographies employs ultrashort laser pulses to produce laser-induced periodic surface structures (LIPSS) that often result in...
Patent
A method of remanufacturing a cylinder head comprises the steps of removing material from the cylinder head around at least a portion of a crack in the cylinder head to form a slot, and applying a compound material using direct laser deposition to fill the slot. The direct laser deposition includes performing a pre-scanning operation at a first las...
Article
Full-text available
Correction for ‘Femtosecond laser ablation of transparent microphotonic devices and computer-generated holograms’ by Tawfiq Alqurashi, et al. , Nanoscale , 2017, 9 , 13808–13819.
Article
Fresnel zone plates (FZPs) have been gaining a significant attention by industry due to their compact design and light weight. Different fabrication methods have been reported and used for their manufacture but they are relatively expensive. This research proposes a new low-cost one-step fabrication method that utilizes nanosecond laser selective o...
Article
Femtosecond laser ablation allows direct patterning of engineering materials in industrial settings without requiring multistage processes such as photolithography or electron beam lithography. However, femtosecond lasers have not been widely used to construct volumetric microphotonic devices and holograms with high reliability and cost efficiency....
Article
Laser microprocessing is a very attractive option for a growing number of industrial applications due to its intrinsic characteristics, such as high flexibility and process control and also capabilities for noncontact processing of a wide range of materials. However, there are some constrains that limit the applications of this technology, i.e., ta...
Article
Full-text available
Micro cell structures of different sizes were patterned using a nanosecond near-infrared laser source on Al2024 aluminium alloy plates with 2 mm thickness. The influence of laser parameters on the shape and size of the produced patterns were studied together with the evolution of wettability properties over time for different storage conditions. Sa...
Article
Full-text available
The paper reports an investigation into the functional response of textured surfaces with different designs that incorporated arrays of micro-dimples and grooves (40μm diameter/width and 15μm depth for both patterns) produced on tungsten carbide (WC) blocks by employing nanosecond (ns) and femtosecond (fs) lasers. In particular, the tribological pe...
Article
Full-text available
Optical diffusers are widely used in filament lamps, imaging systems, display technologies, lasers, and Light Emitting Diodes (LEDs). Here, a method for the fabrication of optical diffusers through femtosecond laser machining is demonstrated. Float glass surfaces were ablated with femtosecond laser light to form nanoscale ripples with dimensions co...
Article
Full-text available
Laser polishing of various engineered materials such as glass, silica, steel, nickel and titanium alloys, has attracted considerable interest in the last 20 years due to its superior flexibility, operating speed and capability for localised surface treatment compared to conventional mechanical based methods. The paper initially reports results from...
Article
This article presents a systematic approach for assessing the maturity of manufacturing technologies. A methodology is proposed that is based on modelling the capability of the individual processes and technology interfaces between them. It is inspired by a capability maturity model which has been applied successfully in the field of software engin...
Article
Full-text available
This article presents an investigation of the machining response of metallurgically and mechanically modified materials at the micro-scale. Tests were conducted that involved micro-milling slots in coarse-grained Cu99.9E with an average grain size of 30 µm and ultrafine-grained Cu99.9E with an average grain size of 200 nm, produced by equal channel...
Conference Paper
The most important requirements in the laser drilling of high aspect ratio micro holes are the throughput and quality, i.e. geometrical accuracy and minimum HAZ. To address these requirements, the paper presents a new laser drilling method that can increase the achievable aspect ratios by a factor of two at least. This method is based on a simple c...
Article
Full-text available
This paper presents two W-band waveguide bandpass filters, one fabricated using laser micromachining and the other 3-D printing. Both filters are based on coupled resonators and are designed to have a Chebyshev response. The first filter is for laser micromachining and it is designed to have a compact structure allowing the whole filter to be made...
Article
Full-text available
The broader use of laser micro-processing technology increases the demand for executing complex machining and joining operations on free-from (3D) workpieces. To satisfy these growing requirements it is necessary to utilise 3D scanheads that integrate beam deflectors (X and Y optical axes) and Z modules with high dynamics. The research presented in...
Article
Titanium oxides have a wide range of applications in industry, and they can be formed on pure titanium using different methods. Laser-induced oxidation is one of the most reliable methods due to its controllability and selectivity. Colour marking is one of the main applications of the oxidation process. However, the colourizing process based on las...
Conference Paper
The industrial demand for product miniaturization has resulted in new designs that integrate multi-scale high aspect ratio functional features. Laser micro-machining is a very attractive solution for producing complex components that can address these growing industrial requirements. The research in this paper proposes a two-sides laser micro-machi...
Article
The advances in the Terahertz (THz) technology drive the needs for the design and manufacture of waveguide devices that integrate complex 3D miniaturised components with meso- and micro- scale functional features and structures. Typical dimensions of the waveguide functional structures are in the range from 200 um to 50 um and dimensions decrease w...
Article
This article reports a follow-up research to investigate further the component technologies of a cost-effective manufacturing route designed to achieve function and length scale integration in products. The route employs a viable master-making process chain that integrates compatible and at the same time complementary, structuring and replication t...
Article
Full-text available
Laser micro-machining (LMM) is an attractive manufacturing process due to its intrinsic machining characteristics such as such as non-contact processing and capabilities to machine complex free-form surfaces in a wide range of materials. Nevertheless, state-of-art LMM platforms still do not offer the repeatability, reproducibility and operability o...
Article
Full-text available
Component technologies of laser micro machining systems are key factors affecting their overall performance. The effects of these technologies on accuracy, repeatability and reproducibility (ARR) in different implementations of such systems have to be investigated to quantify their contributions to the overall processing uncertainty, especially tho...
Article
Full-text available
Laser directed patterning of carbon nanotubes-based buckypaper for producing a diffractive optical device is presented here. Using a laser ablation method the buckypaper was patterned into a binary Fresnel zone plate lens. Computational modelling was performed which revealed excellent focusing performance of the lens for both visible and THz radiat...
Article
An investigation into rectangular waveguide filters with open slots on the broad side walls is reported. This type of waveguide filter eliminates the need for direct contact between the two waveguide halves and intentionally leaves a gap in the middle of broad side walls. For X-band (8.2-12.4 GHz) waveguides, such a gap can be nearly as wide as 9%...
Article
Full-text available
Laser micro-machining is a promising manufacturing solution for fabricating complex micro-engineering products in wide range of materials that incorporate different multi-scale functional features. Optical beam deflector systems are key components in laser micro-machining systems, and they are one of the main factors determining the processing spee...
Article
Full-text available
A novel process chain for serial production of polymer-based devices incorporating both micro- and nano-scale features is proposed. The process chain is enabled by the use of Zr-based bulk metallic glasses (BMG) to achieve the necessary level of compatibility and complementarity between its component technologies. It integrates two different techno...
Article
Full-text available
This paper reports an investigation of material microstructure effects on tool wear in micro-scale machining of multi-phase materials. A new generic approach is proposed to estimate the tool wear that utilises empirical data about the effects of micro milling process on cutting edge radius. Experiments were conducted to study independently the infl...